Radionuclide assessment of myocardial injury in a heterotopic rat heart transplant model

Sensitivity of scintigraphy with 111In-lymphocytes for detection of cardiac allograft rejection

We recently demonstrated the feasibility of noninvasive detection of cardiac allograft rejection after administration of indium-111-labeled lymphocytes. To determine the sensitivity and specificity of the technique, as well as its value for delineating the severity of rejection, we studied 16 dogs with heterotopic thoracic cardiac allografts. Five animals were evaluated while exposed to immunosuppressive agents. Animals were scanned sequentially after administration of 100-400 microCi of indium-111-labeled autologous lymphocytes. Myocardial lymphocyte infiltration was expressed as the indium excess (IE), defined as the ratio of indium activity of the transplant or native heart compared with that in blood. Scintigraphic results were compared with characteristics of simultaneously obtained endomyocardial biopsies. Among 17 biopsy documented episodes of rejection, 16 were detected scintigraphically. Among 18 biopsies with no evidence of rejection, scintigraphy was uniformly negative. Thus, the sensitivity and specificity of scintigraphy were 94 and 100%, respectively. Biopsies graded as showing no rejection were associated with an IE of 0.3 +/- 0.5 (+/- SD); those graded as mild, 2.8 +/- 1.7; those as moderate, 10.7 +/- 7.2; and those graded as indicative of severe rejection, 14.2 +/- 4.5. Thus, scintigraphy with indium-111-labeled lymphocytes sensitively and specifically detects cardiac allograft rejection and delineates the intensity of the rejection process. It should be useful clinically for assessing potential allograft rejection noninvasively.

Noninvasive detection of rejection of transplanted hearts with indium-111-labeled lymphocytes

To determine whether cardiac transplant rejection can be detected noninvasively with indium-111 (111In)-labeled lymphocytes, we studied 11 dogs with thoracic heterotopic cardiac transplants without immunosuppression and five dogs with transplants treated with cyclosporine (10 mg/kg/day) and prednisone (1 mg/kg/day). All were evaluated sequentially with gamma scintigraphy after administration of 150 to 350 muCi of autologous 111In-lymphocytes. Technetium-99m-labeled red blood cells (1 to 3 mCi) were used for correction of radioactivity in the blood pool attributable to circulating labeled lymphocytes. Lymphocyte infiltration was quantified as the ratio of indium in the myocardium of the transplant or native heart compared with that in blood (indium excess, IE). Results were correlated with mechanical and electrical activity of allografts and with histologic findings in sequential biopsy specimens. In untreated dogs (n = 11), IE was 15.5 +/- 7.0 (SD) in transplanted hearts undergoing rejection and 0.4 +/- 1.1 in native hearts on the day before animals were killed (p less than .01). In dogs treated with cyclosporine and prednisone (n = 5), IE was minimal in allografts during the course of immunosuppression (0.8 +/- 0.4) and increased to 22.9 +/- 11.1 after immunosuppression was stopped. Scintigraphic criteria of rejection (IE greater than 2 SD above that in native hearts) correlated with results of biopsies indicative of rejection and appeared before electrophysiologic or mechanical manifestations of dysfunction. Thus infiltration of labeled lymphocytes in allografts, indicative of rejection, is detectable noninvasively by gamma scintigraphy and provides a sensitive approach potentially applicable to clinical monitoring for early detection of rejection and guidance for titration of immunosuppressive measures.